The present invention relates to enhanced detection of pulses in the presence of noise and spurious signals.
Signal pulses of known carrier frequency are used in a variety of situations for communication, object detection, and object location, as well as for other purposes. To the extent that the signal pulses remain in relatively undistorted and of significantly higher amplitudes than background noise, pulse detection can be accomplished with relative ease and simplicity. However, there are many situations in which it is necessary to reliably detect communication pulses contaminated with random noise of significant amplitude relative to the amplitude of the communication pulse. In such situations, simple amplitude and/or frequency discrimination may not provide reliable pulse detection, and other more sophisticated detection are required.
One such technique is described in U.S. Pat. No. 4,038,540 issued to James L. Roberts and assigned to the same assignee as is the present invention. This patent discloses an apparatus for detecting a communication pulse of known carrier frequency, which pulse may be distorted by random noise, by correlating the received communication pulse with a reference signal having a repetition rate equal to the carrier frequency. Correlation is accomplished by multiplying the received communication pulse with each of quadrature components of the reference signal and sampling the product signal to provide binary sample pulse trains which are supplied to a pair of shift register accumulators. Reversible counters and associated logic determine the differences in the numbers of samples of non-corresponding binary values in each of the shift registers, and provide counts which are added to produce a moving correlation signal which indicates presence of a communication pulse when it exceeds a predetermined threshold.
The detection circuitry of prior art systems such as that shown in U.S. Pat. No. 4,038,540, have a time-of-arrival uncertainty, the extent of which is determined by the amount that the communication pulse is distorted by noise.